(1) Field of the Invention
This invention relates to a thixotropic, low solvent, non-hazardous, biodegradable cleaning composition intended for use in the cleaning of aircraft wheel wells and to a method for applying the cleaning composition.
(2) Description of the Prior Art
It has long been a problem in the formulation of cleaning compositions to have a cleaning composition which is environmentally sound as well as effective from a cleaning standpoint. D-limonene, a by-product of the citrus industry, has been found to be an effective cleaning and degreasing solvent. However, D-limonene by itself has other problems. Thus, efforts have been made to develop cleaning compositions based upon D-limonene which meet safety and environmental concerns. U.S. Pat. No. 4,511,488 to Matta illustrates one such cleaning composition based upon D-limonene. The Matta cleaning composition contains D-limonene, a surface active agent selected from the group consisting of anionic, nonionic and mixed anionic-nonionic surfactants, and a coupling agent, suitably a glycol or a lower alkyl glycol ether.
Another cleaning composition containing D-limonene is illustrated in U.S. Pat. No. 5,213,624 to Williams. The Williams cleaning composition contains a terpene solvent such as D-limonene, an aliphatic glycol monoether co-solvent such as dipropylene glycol monomethyl ether, a mixture of nonionic surfactants selected from (1) a capped alkylphenol ethoxylate or an ethoxylated higher aliphatic alcohol, and (2) a fatty acid alkanolamide, and water. Neither the Matta composition nor the Williams composition is intended to act as a cleaning composition for cleaning aircraft wheel wells.
U.S. Pat. No. 5,324,443 to Arif illustrates a biodegradable aqueous filter cleaner formulation containing carboxylic acid and/or a salt thereof, a nonionic biodegradable surfactant based on oxyalkylated linear alcohols, and a water soluble organic solvent.
Existing cleaners for cleaning aircraft wheel wells are formulated with an aromatic solvent content of up to 10% and a total solvent content of 20 to 32%. The presence of these constituents gives rise to environmental concerns. Of primary concern is the aromatic solvent content in these products. These solvents are cited in the 1990 Clean Air Act as hazardous air pollutants (HAPs), and are targeted for elimination from aircraft maintenance operations in 1997 under the National Emission Standards for Hazardous Air Pollutants. Aromatics also have low permissible exposure limits (PELs) and contribute to workplace health hazards. Finally, aromatic solvents have an extremely low level of biodegradability. This causes concern from a waste treatment standpoint or if the product were to migrate into natural waterways.
Ethylene class glycol ether coupling solvents, included in existing products to improve solubility and stability of the components, are also HAPs and have PELs on the order of 100 parts per million (ppm).
Other solvents may be present in these products, subject to variation by manufacturer, to bring the total solvent content to a maximum of 32%. Most solvents used for this purpose are classified as volatile organics compounds (VOCS) and are subject to local air emission regulations. For example, it is now necessary at the North Island Naval Aviation Depot in California to use aircraft maintenance products containing less than 10% total VOCs in the use dilution. This allows the products to be exempt from Rule 66 of the San Diego County air pollution control regulations.